The present invention generally relates to a diode unit, and more particularly, to a laser diode for use in an electrical or electronic equipment.
Conventionally, in the field of laser diodes, there have been employed a so-called can-seal type and a unit type. As shown in cross sectional views of FIGS. 8 and 9, an example of a known unit type laser diode 41 is shown which generally includes a substrate 42, and a laser diode chip 49 die-bonded on the substrate 42 through a sub-mount 43, with a photodiode being incorporated in the sub-mount 43 as a monitor element 47.
The monitor element 47 referred to above is arranged to receive laser light emitted from a rear cleavage face 49b of the laser diode chip 49. Based on the light receiving current (i.e. monitor current) of the monitor element 47, driving current for the laser diode chip 49 is controlled by an APC (automatic phase control) circuit so as to allow laser light of the laser diode chip 49 to reach a predetermined value.
On the sub-mount 43, aluminum wirings 45 and 46 connected to the laser diode chip 49 and the monitor chip 47 are formed so as to be bonded to leads 54a and 54b on the flexible circuit 54 by wires W.
In the conventional laser diode 41 as described above, because a front cleavage face 49a of the laser diode chip 49 has a problem of flatness, the characteristics of the laser beam emitted from the front cleavage face 49a may be adversely affected.
Another disadvantage of the conventional laser diode is that, when the laser diode 41 is formed into an open construction without covering, the front cleavage face 49a is exposed to atmosphere and the state of its surface is altered by moisture in the air. As a result, the convention laser diode is inferior in resistance against the environment. In the case of the laser diode of the can-seal type, such a problem does not readily take place because the laser diode is sealed. However, another problem exists that a sufficient size reduction is difficult to be achieved.